Three types of cystinosis are recognized: nephropathic (infantile) cystinosis, late-onset (intermediate) cystinosis, and benign cystinosis. Our clinical experience suggests that each of these three types may include more than one phenotype. It is possible that attempts to delineate the exact defect in this disease and to evaluate experimental therapies have been confused by failure to distinguish between the multiple types of this disease. We propose to investigate this problem in two ways. First, we will characterize cultured skin fibroblasts and cultured lymphoblasts from such patients. These studies will include growth characteristics of the cells, free (acid soluble) cystine content of the cells, and kinetics of S35 cystine incorporation into glutathione and protein by the cells. Correlation will be sought between these results and the clinical findings. Secondly, we will use somatic cell hybridization as a technique to search for complimentation between the various cell types. BIBLIOGRAPHIC REFERENCES: Oshima, R. G., W. J. Rhead, J. G. Thoene, and J. A. Schneider: Cystine Metabolism in Human Fibroblasts: Comparison of Normal, Cystinotic, and gamma-glutamylcysteine Synthetase-deficient Cells, J. Bio. Chem., 251:4287, 1976. Thoene, J. G., R. G. Oshima, J. C. Crawhall, D. L. Olson, and J. A. Schneider: Cystinosis: Intracellular Cystine Depletion by Aminothiols In Vitro and In Vivo, J. Clin. Invest., 58:180, 1976.